Heretofore, measurement of bonding such as an intermolecular interaction between biomolecules such as an antigen-antibody reaction, or an intermolecular interaction between organic molecules has, in general, been carried out using a label such as a radioactive substance, a phosphor. The labeling takes a lot of work, and, in particular, a labeling method to a protein is sometimes complicated, or the characteristics of a protein were sometimes changed due to the labeling. In recent years, as a means to detect a bonding between biomolecules or organic molecules easily and directly without using the label, the RIS (reflectometric interference spectroscopy) method utilizing the change of interference color of optical film has been known. Its basic principle is described in Patent Document 1, Non-patent Document 1, or the like.
When describing briefly the RIS method, detector 100, which is shown in FIG. 6, is used in this method. As it is shown in FIG. 6a, detector 100 has substrate 102, and optical film 104 is arranged on substrate 102. When white light is irradiated on detector 100 with these conditions, the spectral intensity of the white light itself is shown by solid line 106, and the spectral intensity of the reflected light of the white light is shown by solid line 108, as they are shown in FIG. 9. When the reflectance is determined from each of spectral intensities of the irradiated white light and its reflected light, reflection spectrum 110 shown by a solid line is obtained, as it is shown in FIG. 10.
For detecting the intermolecular interaction, ligand 120 is arranged on optical film 104, as it is shown in FIG. 6b. When ligand 120 is arranged on optical film 104, optical thickness 112 is changed and thereby the optical path length is changed, and then the interference wavelength is also changed. Namely, the peak position of the spectral intensity distribution of the reflected light is shifted, and as a result, as it is shown in FIG. 10, reflection spectrum 110 is shifted to reflection spectrum 122 (refer to the dotted line). In this situation, when a sample solution is poured on detector 100, ligand 120 of detector 100 is bonded with analyte 130 in the sample solution, as it is shown in FIG. 6c. When ligand 120 is bonded with analyte 130, optical thickness 112 is moreover changed, and then, as it is shown in FIG. 10, reflection spectrum 122 is shifted to reflection spectrum 132 (refer to the dashed-dotted line). Then, it is designed so that, by detecting the amount of change between the peak wavelength (bottom peak wavelength) of reflection spectrum 122 and the bottom peak wavelength of reflection spectrum 132, the intermolecular interaction can be detected.
When observing the transition of changes of the bottom peak wavelength over time, as it is shown in FIG. 11, a change of the bottom peak wavelength by ligand 120 can be confirmed at point of time 140, and further a change of the bottom peak wavelength by bonding between ligand 120 and analyte 130 can be confirmed.